Accessory drive systems for internal combustion engines typically include rotatable components, such as a fan and/or other high rotational inertia components, which are driven by the engine via a pulley and flexible belt arrangement, hydraulic pump, chain drive, or the like. In one such system, a crankshaft pulley is rotatably driven by the engine crankshaft, and a rotatable component, such as a fan hub rotor of a fan assembly, is driven by an accessory pulley, and the crankshaft pulley drives the accessory pulley via a flexible belt rotatably connected therebetween.
In order to maintain appropriate belt tension over time and over a wide range of operating conditions, accessory drive systems of the foregoing type may include a belt tensioner that is typically provided in the form of a pulley or wheel that exerts a biasing force on the belt to maintain a desired belt tension. It is desirable with such accessory drive systems to control operation of the engine so as to avoid belt tensioner instability conditions, such as excessive accumulation of the belt in the region between rotating components, typically referred to as a span, resulting in the tensioner rotating through its full travel, which may cause the maximum load capacity of the belt tensioner to eventually be exceeded.